The present invention relates to the preparation of polyolefin-based graft copolymers comprising a first long chain branched polyolefin block and one or multiple polymer side chains, the intermediate products and the processes to obtain these products.
Commercially available polyethylene and polypropylene prepared using standard procedures with Ziegler-Natta or single-site catalysts have a predominantly linear molecular structure. Although linear polyolefins have many desirable physical properties, they show a variety of melt processing shortcomings, especially the single-site prepared ones having narrow molecular weight distributions, which typically have a low melt strength. Low melt strength is a problem because it causes local thinning in melt thermoforming, relative weakness in large-part blow molding and flow instabilities in co-extrusion of laminates.
One way of overcoming the shortcomings of linear polyolefins is by means of branching, viz. the provision of polymer side chains extending from the polyolefin backbone.
Despite their ubiquitous presence in our society, polyolefins such as polyethylene and polypropylene are not appropriate for several applications as a consequence of their inherently nonpolar character. This nonpolar character is the reason for the poor adhesion, printability and compatibility that can restrict their efficacy. Hence, it is further desirable to prepare polyolefins bearing for example polar groups so to ensure a good adhesion and printability.
In the prior art copolymers have thus been prepared and considered to overcome the shortcomings of polyolefins mentioned above. However, the preparation of these copolymers is often complicated and cumbersome. Moreover, most preparation methods lack flexibility.
The present invention is directed towards an easy, catalyst-compatible, relatively inexpensive and safe process that can be used for large scale preparation of polyolefin-based graft copolymers comprising a first long chain branched polyolefin block and one or multiple polymer side chains.